1. Technical Field
The present invention relates to a buffer circuit, an amplifier circuit, and a test apparatus. More particularly, the present invention relates to a buffer circuit that generates an output signal of which a signal level is restricted to a predetermined range, an amplifier circuit that uses this buffer circuit, and a test apparatus that uses this amplifier circuit.
2. Related Art
As a circuit that restricts a level of a signal, there has been known a circuit in which a forward-direction diode and a backward-direction diode are provided between a signal transmission path and a ground potential, for example. Moreover, a resistance is formed on the signal transmission path. Such a circuit can restrict a level of a signal to a range prescribed with forward-direction and backward-direction threshold voltages of the diodes. Moreover, the restriction range of the signal level can be adjusted by serially providing voltage sources in each diode, or the like.
However, in the above-described clamp circuit, input impedance and output impedance are determined by the resistance formed on the signal transmission path. For this reason, it is difficult to sufficiently increase the input impedance or to sufficiently decrease the output impedance.
Moreover, a frequency band of a signal passing through the above-described clamp circuit is restricted in accordance with a time constant determined by the resistance on the signal transmission path and junction capacitance of the diodes. For this reason, it is difficult to restrict a signal level of a high-frequency signal.
Moreover, it may be considered to combine a buffer circuit or an amplifier circuit with the above-described clamp circuit in order to restrict a signal level output from the buffer circuit or the amplifier circuit. However, the buffer circuit and the amplifier circuit using this clamp circuit also have a problem similar to the above-described problem.